The tropical Atlantic has been putting on quite the show over the last couple of weeks of Hurricane Harvey (Category 4). . .I’m sure you heard of that one, followed by Irma (Category 5), Jose (Category 4), and Katia (Category 2). Katia made landfall last night in Mexico and now we continue our focus on Irma and Jose. Why is it so active? A few reasons: warm ocean (sea surface temperature and high ocean heat content), lack of a true El Nino Southern Oscillation (ENSO) signal, though it looks like a weak La Nina, little to no shear throughout much of the basin, a lack of dust from the Sahara, and a strong Azores high. Oh yeah, on top of that, we have the Madden-Julian Oscillation (MJO) more or less stuck in favorable phases for the Atlantic (8, 1, 2, 3) and forecasts suggest that stays in place for a while.

ECMWF MJO verification and forecast courtesy of the Climate Prediction Center (CPC). Click here to open in a new window.

GEFS MJO verification and forecast courtesy of CPC. Click here to open in a new window.

One product I noticed in use at the Ocean Prediction Center (OPC) on Friday, 09/08/17 was the GOES-16 Daytime Convection RGB, so I thought this would be a nice opportunity to show you all three current Atlantic systems with a comparison to the 10.3 µm “clean” channel.

GOES-16 Daytime Convection RGB of Hurricane Irma valid 1100 UTC to 2300 UTC on 09/08/17. *Preliminary, Non-Operational Data* Click here to open in a new window.

Note the bright yellow coloring that highlights, new convection with smaller ice particles indicating strong overshooting tops in the outer rainbands, while the main central dense overcast (CDO) surrounding the eye also gets brighter. This indicates that after the eyewall replacement cycle ended, the new eyewall started to contract and strengthen (winds at this time were 155 mph, but shortly after this strengthened to 160 mph.

GOES-16 10.3 um “clean” infrared window channel similar to the previous animation of Hurricane Irma. *Preliminary, Non-Operational Data* Click here to open in a new window.

Notice that the 10.3 µm “clean” window shows us the brightness temperature of the coldest cloud tops. Although you can see the new overshooting tops, as those thunderstorms rotate around the CDO, it gets more difficult to identify the newer, important convection.

GOES-16 Daytime Convection RGB for Hurricane Jose valid 1000 UTC to 2045 UTC on 09/08/17. *Preliminary, Non-Operational Data* Click here to open in a new window.

By contrast, notice how compact Hurricane Jose became as it strengthened to a 150 mph Category 4 hurricane on Friday (09/08/17). Again, the beginning of the animation shows plenty of yellows that indicate new convection, wile the older convection fades to oranges, then reds. Also notice how the CDO becomes more yellow as the eye becomes cleaner and the storm takes on a more donut structure, even with the strong outflow channel to the northeast that makes the storm look lopsided. Could this RGB be helpful in identifying CDO changes? Or help with indicating eyewall replacement cycles (ERCs) in conjunction with microwave imagery?

GOES-16 10.3 um “clean” infrared imagery similar to the previous animation of Hurricane Jose. *Preliminary, Non-Operational Data* Click here to open in a new window.

Again, to contrast the Daytime Convection RGB, the above 10.3 µm animation shows very cold cloud tops, but the newer convection starts to blend in with the CDO over time. Do you see other differences?

GOES-16 Daytime Convection RGB of Hurricane Katia valid 1200 UTC to 2357 UTC on 09/08/17. *Preliminary, Non-Operational Data* Click here to open in a new window.

Finally, Hurricane Katia was very small in comparison with the other two hurricanes, but notice there are differences in the intensity of the convection on Friday (09/08/17). What do you see in the imagery? There are less yellows than in Irma or Jose, yet the storm intensified to a Category 2, 90 kt (105 mph) hurricane prior to landfall on Friday evening. The warming clouds and less cold, newer convection may have been due to dry air entrainment due to the close proximity to mountainous land nearby and a weak trough to the north.

GOES-16 10.3 um “clean” infrared imagery similar to the previous animation of Hurricane Katia. *Preliminary, Non-Operational Data* Click here to open in a new window.

How does the 10.3 µm imagery above contrast with the Daytime Convection RGB?

So, what is steering Irma? What about Jose and Katia? Well, I’m glad you asked. . .

GOES-16 Air Mass RGB image valid at 0900 UTC 09/09/17. *Preliminary, Non-Operational Data* Click here to open in a new window.

The GOES-16 Air Mass RGB image (courtesy of NASA SPoRT) above with my crude drawings show a rough idea of the players affecting the steering flow around the three hurricanes. Katia has made landfall as it was pushed southwest due to the old cold frontal boundary (responsible for the cool air in most of the country) along with a disturbance highlighted in the yellow circle. This disturbance will close off over the Tennessee Valley area and help to pull Hurricane Irma north, then northwestward in the next 48 hours. Finally, Jose (east of the Lesser Antilles) will be pulled north through a weakness in the ridge due a weakness created by the Tropical Upper Tropospheric Trough (TUTT in the yellow “T”) to the northeast and Irma’s broad circulation. Since the current trough over the northeast U.S. moves east/northeast and the central Atlantic TUTT remains stationary, Irma gets left behind in the southeast U.S., but weakening after landfall, while Jose gets left behind and may perform a tight anticyclonic loop before “possibly” moving northwest. We’ll deal with Jose later. . .

I have included the GOES-16 Air Mass RGB and 7.3 µm low-level water vapor animations below so you can get a better feel of the overall pattern.

On the morning early of 04/06/17, TAFB forecasters noted a nice V-pattern to convection at the tail end of a front in the northeast Gulf of Mexico. The increased temporal and spatial resolution of GOES-16 compared to the GOES-13 (east) provided more details on the organization and maintenance of the convective line that would otherwise have been analyzed.

Hugh Cobb (TAFB Branch Chief) noted: “We also looked at the Red VIS Band 2 for this event. The VIS imagery was more striking in that you could see the shadows of the high cirrus cast on the lower cloud deck in the animation and the “beavertail” of of the low clouds feeding into and maintaining the deep convection.”

Jorge Aguirre-Echevarria (TAFB Forecaster) noted that “the striking cloud/convective signature and associate lightning activity observed that day over the waters of the far southern Gulf of Mexico.” In particular, these events are rather rare at such a low latitude in the TAFB Offshore Zones. The GOES-16 10.3 μm infrared imagery proved to be very helpful in seeing the overshooting tops and the cold cloud canopy temperatures which signified the activity would persist west of Key West, FL.

As you can see in the GOES-13 infrared animation above, the structure of Matthew has gone through a few changes today with some northerly shear blunting the northern portion of the hurricane, although this hasn’t lead to any notable weakening as of yet. In the last couple of frames, very strong convection fires again as the hurricane is approaching Grand Bahama. Also of note is the strong area of convection that fired to the northeast of Matthew today, though not as strong as what was seen in the Caribbean over the weekend.

The GOES-13 infrared imagery with GLD-360 15-minute lightning density overlaid shows a couple distinct areas of lightning activity, the aforementioned convection to the northeast and another area in the northeast eyewall. This latter area has been pulsing all day and may suggest that the shear mentioned earlier was being fought off by the deep pulses of convection. Note that this area passed over the western portion of Providence Island and is getting ready to move ashore in southwest Grand Bahama. This is where the aircraft is showing the strongest winds (near 120 kts or 140 mph).

NUCAPS sounding (black circle on above image) showing some drying and warming above 700 mb to the north of Hurricane Matthew. Note that this isn’t a clean sounding since there are clouds in the scene, but the multiple warm layers are certainly interesting.

So, where did this shear originate from? I haven’t quite found the source, but I did pull up a NOAA Unique Combined Atmospheric Profiles (NUCAPS) sounding that may not be the most representative of the northern portion of the cyclone due to clouds, but does show an interesting drying at mid-levels. Note there are no winds as this is a satellite-borne sounding looking down, not to be confused with a raob.

Another product that has been available to forecasters at the National Hurricane Center, Weather Prediction Center, and NESDIS Satellite Analysis Branch is the GOES-R Rain Rate/QPE product provided by Bob Kuligowski at NESDIS. These are 15 minute rain rates that are derived using infrared brightness temperatures, then calibrated with microwave imagery. Note the values near the eyewall approaching 1″-1.50″ per 15 minutes!!!

The 7-day QPE accumulation image above shows many values over western Haiti and eastern Cuba approaching and exceeding 20″, which might even be conservative in the higher terrain areas. Note other interesting features like the rain shadow in northern Dominican Republic and amounts that exceed (then re-accumulate) 20″-45″ near where Matthew slowed north of Columbia. The now infamous “convective blob” is where the largest totals are located and might be reasonable for this case considering the extreme lightning and intensely cold cloud tops.

This final animation shows the very intense lightning activity associated with the inner core organization and infamous “convective blob” that was trailing Hurricane Matthew through the southern Caribbean. The persistent lightning in the northern eyewall is interesting in that it’s rather atypical for rapid intensification in Atlantic hurricanes. Meanwhile, the lightning associated with the blob is very intense at 15 minute increments and helps support those extreme rain amounts that fell over the Caribbean.

While West African tropical waves continue to propagate out into the tropical North Atlantic, none are expected to develop into a tropical cyclone soon. Today, the 2:00 PM EDT NHC Two-Day Graphical Tropical Weather Outlook shows one of these waves accompanied by a broad low pressure system, which particularly looks impressive on satellite imagery (see image below). Still, environmental conditions are not too favorable for a cyclone to form.

NHC Two-Day Graphical Tropical Weather Outlook on July 29 at 2:00 PM EDT depicting a West African tropical wave accompanied by a broad low pressure system with low chance of cyclone formation

Generally, tropical waves are accompanied with areas of disturbed weather that along with other dynamics of the atmosphere (that include climatological and synoptic conditions) could lead to cyclogenesis. One of the main favorable atmospheric conditions for tropical cyclone development is sustained, deep, moist convection. However, constant and extensive episodes of Saharan Air Layer (SAL) outbreaks are disrupting the formation of a nearly-saturated middle troposphere, which has contributed to the overall weak tropical waves pattern.

Below, enhancements of Meteosat satellite imagery with the TAFB surface analysis overlaid depict various tropical waves being affected by SAL outbreaks during mid July. The imagery show how the dry air (orange and yellow shades) and dust (pink shade) associated with this Saharan airmass cover a large part of the waves environment, thus acting to suppress any convection originating in the marine layer.

First of all, welcome to the brand new “Satellite Liaison Blog”! After some consideration, the other satellite liaisons and I decided to revamp this blog to fit the Proving Ground activities at all of the National Weather Service National Centers and Field Offices. We hope to keep you informed and spur excitement about new satellite products as we move closer to the launch of GOES-R and JPSS-1. Please bookmark the site (satelliteliaisonblog.wordpress.com) for future reference, although you will be forwarded here from the old site name for a year.

Now on to this week’s storm of interest …

Tropical Cyclone Hellen formed in the northwest Indian Ocean between Mozambique and Madagascar on 03/28/14. Hellen rapidly intensified from a 60 kt (70 mph) tropical storm to a 130 kt (150 mph) Category-4 tropical cyclone in 18 hours (satellite-based)! Since the Atlantic hasn’t shown us a strong hurricane (Category 3+, but safely out at sea) in a few years, we haven’t had many opportunities to look at hurricanes with some of the new Red Green Blue (RGB) products that NASA SPoRT and CIRA have been providing the Proving Grounds. Therefore, we will use Hellen for this first look.

SEVIRI (Met-10) RGB Air Mass animation of TC Hellen.

The first RGB animation above is the Air Mass product which has received much attention on this blog, especially related to extratropical cyclones. The main feature of interest with Hellen is the very pronounced anti-cyclone surrounding the storm as evidenced by the cirrus clouds being pulled away from the cyclone. This is excellent outflow and allowed for maximum evacuation of air from the center, helping to induce the rapid intensification cycle. The other aspect of the imagery that stands out is the warm, moist air mass in the green coloring. Any drier air is located well away from the storm to the east and southwest. This product’s strongest attribute is identifying the air masses and potential upper-level systems (red coloring) that could affect tropical cyclones.

SEVIRI (Met-10) RGB Day Convection animation for TC Hellen.

The RGB Day Convection product above can be used to differentiate new, building convection from dying convection or cirrus clouds. The yellow colors indicate areas of new convection with mixed phase hydrometeors (convective bands or in the eyewall), while the red to purple coloring (areas away form the cyclone’s center) indicates weakening convection and cirrus, which contain more ice. I included the night-time images to show a significant limitation to using this product. . .it’s only available during the day.

SEVIRI (Met-10) RGB Day Microphysics animation of TC Hellen.

The final RGB product that will be introduced here is the RGB Day Microphysics. This is somewhat similar to the Day Convection product, but the different shades of color indicate different hydrometeor phase and size.

These new RGBs were introduced to the National Hurricane Center near the end of last season as a way of monitoring the stages of convection during genesis, then maintenance of tropical cyclones. These will be evaluated more during the 2014 Atlantic Hurricane Season.

If you would like more information on these products, please visit http://www.eumetrain.org or http://weather.msfc.nasa.gov/sport/training/

Remember, the East Pacific hurricane season starts on 05/15/14 and the Atlantic hurricane season starts on 06/01/14.

Thank you for reading!

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